Brazed cylinder muff



May 14, .1946; A. A. MERRY 2,400,157

BRAZED CYLINDER MUFF Filed Sept. 11, 1943 2 Sheets-Sheet 1 INVENTORflriiaazrflj ferry May 14, 1946; A. A. MERRY BRAZED CYLINDER MUFF FiledSept. 11, 1943 2 Sheets-Sheet 2 l "mini": I

Patented May 14, 1946 UNITED STATES PATENT OFFICE BRAZEDmERMUFF ArthurA. Merry, West Hartford, Conn., to United Aircraft Corporation, Eastaasignor Hartford,

Conn., a corporation of Delaware Application September 11, 1943, SerialNo. 501,982 2 Claims. (Cl. 257-261) This invention relates toimprovements in heat transferring structure and has particular referenceto an improved heat radiating structure for internal combustion enginecylinders and to an improved method of making the same.

An object of the invention is the provision of an improved unitary heatradiating structure and more particularly such a structure especiallyadapted for use on the cylinders of aircooled engines of the type usedin aircraft.

A further object of the invention is the provision of a cylindricalfinned mufi of the character indicated having improved heat abstractingand radiating characteristics.

A further object of the invention is the provision of a brazed or weldedaluminum cylinder mull. made from sheet metal stampings.

A still further object of the invention is the provision of such a muii'in which the fins are shaped to form the cylinder cowling for directinga cooling stream of air through the fins.

A yet further object of the invention is an improved method of makingaluminum mulls for air-cooled engine cylinders.

Other objects and advantages will be more particularly pointed outhereinafter or will become apparent from the following description.

I In the accompanying drawings,in which like reference characters referto similar parts throughout, several forms of the invention are shownfor purposes or illustration.

In the drawings- Fig. 1 is a fragmentary sectional view of a cylindermuiI embodying the invention;

Fig. 2 is a somewhat similar view on an enlarged scale showing amodified iln construction;

Fig. 3 is a sectional view taken on line 8-3 of Fig. 4 illustrating afurther modified construction.

- Fig. 4 is a sectional view taken on line 4-4 of Fi 3;

Fig. 5 is a view similar to Fig. 3 showing a further modifiedconstruction; and i Fig. 6 is a sectional view showing the mull of Fig.1 associated with an engine cylinder.

Referring to the drawings in detail and particularly to Fig. 6, the heattransferring structure is illustrated as a cylinder muii, generallyindicated at III, mounted on the barrel portion II of an engine cylinderbetween a lower annular shoulder It and the cylinder head portion II.The particular cylinder shown is adapted to, be mounted on the crankcase2| oi a conventional radial type engine used in aircraft, the usualexternal flange II and the stud and nut con- The muff I0 comprises aplurality of generally similar centrally apertured thin discs, or fins,

24 spaced apart by somewhat thicker rings, or spacers, 26 which aresimilarly apertured and extend around the apertures in the discs. Thesediscs and spacing rings are secured together to form a unitary structureas by welding or brazing. The discs 24' which comprise the heatradiating fins of the mufi are made of soft aluminum which has good heatconducting qualities, while the spacers 28 are made of a harder,stronger aluminum alloy. When welded or brazed together the rings andthe contiguous parts of the discs provide a strong sleeve portion forthe muff adjacent the barrel portion I2 01" the engine cylinder which,when the muff is shrunk onto the cylinder barrel, provides intimatecontact between the sleeve of the mud and the barrel of the cylinder asis required to obtain rapid and uniform heat flow from the cylinder tothe mull. The importance of such a firm and uniform connection betweenthe mufi and the cylinder will be evident when it is noted that thebarrel I2 '01 the engine cylinder is very thin, as is customary inaircraft engine practice.

The discs 24 comprising the fins and the rings 26 comprising the spacersmay be bonded together in any suitable manner, as by welding or brazing.A preferred method of brazing the stack of fins and spacers togetherconsists in rolling out sheet aluminum from the billet with a coating ofbrazing material adhering to the surfaces of the sheet from which thefins and rings are stamped.

The fins and spacers are stamped out with the apertures therethroughslightly smaller than the outside diameter of the barrel. The mun isthen assembled with the apertures in the fins and spacers in verticalalignment, preferably about a mandrel. Pressure is then appliedlongitudinally to the sleeve of the mufi' while the mui! is heated tobrazing temperature, at which the brazing material on the surface of thefins and spacers fuses. Pressure is maintained ontheassembledfinsandspacersuntilthemufihal cooled below the bracingtemperature. The inside of the sleeve is then finished to accuratedimension to enable it to be heat shrunk onto the cylinder barrel II ina usual manner.

As a result, a unitary structure is provided in which the fins It whichare of soft aluminum conduct the heat very readily from the cylinderside walls with which their inner surfaces are constantly maintained indirect pressure contact. while the spacers It, being of strongeraluminum alloy, provide the necessary strength to enable the mill! to beshrunk onto the cylinder barrel with sumcient pressure to maintain thisgood heat conducting relationship between the mull and the cylinder.

It will be further noted that as a result of this construction the finscan be spaced more closely together than has been possible with thesolid forged type of muif previously used in which the fins were formedby machining grooves in the form. Moreover, the present construction byutilising soft aluminum material for the fins enablea faster heatconduction from the cylinder wall while permitting as good or evenbetter heat conductivity as the result of the stronger pressure providedby the shrinkage strength of the aluminum alloy spacers between thefins. It will also be noted that considerable saving in material,lncuttingtoolcostsandinlabcrisefiectedby the above described method ofuniting the stamped aluminum fins and spacers into an intesral muff.

In Fig. 2 the fins 24 are provided with indentations, or dimples, 2|located adjacent the outer periphery of the fins. Preferably thesedimples are staggered so that the dimple in one plate is ofiset relativeto the dimple in the next adjacent plate. As shown in Fig. 2 the dimples2| are provided in alternate fins at diiferent distances from thevertical axis of the mufi to provide a radially staggered arrangement,although it will be obvious that all of the fins could be stamped withthe same die and the staggering could be accomplished by assembling thefins in difi'erent angular relation to provide circumferentialstaggerlng of the dimples. The dimples have a slightly flattened bottomsurface It and are of the same depth as the interfin spacing so thateach fin vdll be engaged by the dimple of an adjacent fin. This isespecially important where very thin Ind soft aluminum sheet is used forthe fins. serving not only to prevent vibration of the fins but also tosupport the same adjacent their free outer periphery and preventsagging.

The provision of the dimples It has a further advantage in that itincreases the cooling area The cooling efiect of these dimples isconsiderable since they project into a part of the air stream whichotherwise does not contact the fin area.

In Figs. 3 and 4 a modified fin construction is own in which the heatabstracting eifect of II is made even more efiective. in constructionthe fins a are made of very thin sheet stock and the spacers "a are alsomade thinner so as to provide very close spacing betweenthefins.Hereitwillbenotedthatthe spacers "a have their radial thicknessincreased so as to provide the same strong holding pressure flanges 80which depend therefrom a sufiicient distance to engage the top surfaceof the next lower fin and provide a peripheral support for the latterwhile also closing the interfin space between adjacent fins. Portions ofthese fianges II are cut away at diametrically opposite sides of thecylinder to provide inlet and outlet areas "and It for the airstreampassing across the engine cylinder, the portions of the flanges IIIwhich are not removed constituting in conjunction with the sleeve of themuff, semi-circular air passage means between the fins. In this modifiedconstruction dimples Ila and "b are provided in the fins in two annularrows arranged in staggered relation as indicated in Fig. 3. Also it willbe noted that the dimples of adjacent fins are staggered so that thedimples provide vertical support for the thin fins as well as projectinginto the semi-circular air streams passing between the fins in suchmanner as to cause the air to follow a tortuous path as it passestherebetween.

In Fig. 5 a still further variation of fin con struction is shown. Inthis form of the invention the fins are stamped out with opposedperipheral extensions it which are provided with a series of V-shapednotches it at spaced points along their periphery to'provide a series ofcars 40. These ears are then bent at right angles to the plane of thefin to provide fin cowling similar to that described in'connection withFigs. 3 and 4, it being noted that in bending the ears til the notchesII become closed and permit the ears to form the smooth peripheralflanges shown in full lines in Fig. 5.

As a result of these improvements it will be evident that a cylindermail has been provided which is light in weight, utilizes a minimum ofmaterial and enables softer, better heat conducting thin material to beused than has hereto been possible with the forged type mull. It willalso be evident that this improved construction enables greater heattransier and better distribution of the cooling .air stream due to theprovision of dimples in the fins while also enabling the cylindercowling to be formed integral with the fins and thus also to assist indissipating the heat. It will also be evident that as a result of thebuiltup muif construction from sheet metal stampings any desired spacingof the fins is possible, all limitations as regards machining groovesbeing eliminated. Further, the improved brazed sheet metal constructionand the method of forming the fins and spacers into an integral unit bybrazing results in a considerable saving in labor and material.

While there are shown in the accompanying drawings several embodimentswhich the invention may assume in practice, it will be understood thatthese are shown for purposes of illustration only and that numerouschanges may be made in the construction and arrangement of the partswithout departing from the scope of the invention as defined in thefollowing claims.

Having now described the invention so that others skilled in the art mayclearly understand the same, what it is desired to secure by LettersPatent is as follows:

1. In an air-cooled cylinder for an internalcombustion engine, acylinder barrel and a. heat dissipating muff shrunk thereon, said mufi'comprising a stack of alternately arranged fins and spacers havingaligned apertures therein for receiving said cylinder barrel, the finsof said mufi being formed of soft aluminum having a high ooefilcient ofthermal conductivity and the spacers being formed of harder aluminumalloy, said said cylinder barrel, the tins of said muff comprisingpreformed sheets of thin soft aluminum having a high coemcient ofthermal conductivity and said spacers comprising preformed rings ofthicker sheets of harder aluminum alloy, said fins and spacers beingintegrally united at their contacting surfaces with the apertures inalignment to iorm a sleeve having the inner peripheral edges of bothsaid tins and spacers in pressure engagement with said barrel throughoutthe range of engine operating temperature.

ARTHUR A. MERRY.

